A magnetic disc apparatus is one, which writes or reads information into and from tracks on a surface of a rotating magnetic disc.
A head element used for writing and reading of information into and from the magnetic disc is mounted to a slider, which forms an ABS (Air Bearing Surface) with the magnetic disc. The slider is mounted on a flexible suspension of a rigid arm to be movable between tracks.
The rigid arm is driven by a VCM (Voice Coil Motor) and the head element is moved to a track for recording by a servo mechanism. As the magnetic disc apparatus is increased in recording density, tracks are decreased in width and pitch and therefore, it becomes difficult to move the head element at high speed to a track for recording by VCM single control.
For example, it is difficult for a servo mechanism of VCM single control to accommodate to a frequency band of 2 kHz or more.
As a solution for an improvement in servo frequency band, two-stage actuators have been proposed. With the two-stage actuator, a VCM is used as a coarse movement actuator in a first stage to perform coarse positioning. Thereafter, fine positioning is performed in a second stage.
In the second stage, a micro actuator for driving a slider is provided between a flexible suspension and the slider. By finely displacing the micro actuator, a head element and a recorded track are positioned accurately to realize a high accuracy and a positioning control in high servo frequency bands.
U.S. Pat. Nos. 5,995,334 and 7,382,583B2 are listed as prior arts of micro actuators for two-stage actuator.
A micro actuator described in U.S. Pat. No. 5,995,334 makes use of MEMS (Micro Electro Mechanical Systems) technology to form a fine movement actuator, a drive source of which is provided by electrostatic attraction, to drive a slider.
U.S. Pat. No. 7,382,583B2 discloses a micro actuator, a drive source of which is provided by a piezoelectric element, to drive a slider. Adoption of a piezoelectric element capable of generating a large force makes it possible to increase a construction in stiffness and to improve controllability on disturbance.
However, a micro actuator making use of electrostatic attraction can generate only a relatively small force, with the result that it is necessary to decrease a construction in stiffness. As a result, there are involved problems that a micro actuator is decreased in mechanical resonance frequency, has a low degree of disturbance tolerance, and is decreased in positioning accuracy.
Also, a micro actuator making use of a piezoelectric element involves problems of generation of dust from the piezoelectric element while a magnetic disc is used, or complexity in a process of assembling a piezoelectric element of a bulk material after manufacture of a substrate, on which actuator is put, with the MEMS technology, and a high manufacturing cost.
It is an object of the invention to provide a magnetic disc apparatus comprising a micro actuator for two-stage actuator, which is used for a magnetic disc apparatus capable of realizing a high accuracy and a simple positioning accuracy.